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drm: Document variable refresh properties

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These include the drm_connector 'vrr_capable' and the drm_crtc
'vrr_enabled' properties.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Nicholas Kazlauskas 2018-10-04 14:38:42 -04:00 committed by Alex Deucher
parent 1398958cfd
commit ab7a664f7a
2 changed files with 75 additions and 0 deletions
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7
Documentation/gpu/drm-kms.rst
View file

@ -575,6 +575,13 @@ Explicit Fencing Properties
.. kernel-doc:: drivers/gpu/drm/drm_atomic_uapi.c
:doc: explicit fencing properties
Variable Refresh Properties
---------------------------
.. kernel-doc:: drivers/gpu/drm/drm_connector.c
:doc: Variable refresh properties
Existing KMS Properties
-----------------------

68
drivers/gpu/drm/drm_connector.c
View file

@ -1271,6 +1271,74 @@ int drm_mode_create_scaling_mode_property(struct drm_device *dev)
}
EXPORT_SYMBOL(drm_mode_create_scaling_mode_property);
/**
* DOC: Variable refresh properties
*
* Variable refresh rate capable displays can dynamically adjust their
* refresh rate by extending the duration of their vertical front porch
* until page flip or timeout occurs. This can reduce or remove stuttering
* and latency in scenarios where the page flip does not align with the
* vblank interval.
*
* An example scenario would be an application flipping at a constant rate
* of 48Hz on a 60Hz display. The page flip will frequently miss the vblank
* interval and the same contents will be displayed twice. This can be
* observed as stuttering for content with motion.
*
* If variable refresh rate was active on a display that supported a
* variable refresh range from 35Hz to 60Hz no stuttering would be observable
* for the example scenario. The minimum supported variable refresh rate of
* 35Hz is below the page flip frequency and the vertical front porch can
* be extended until the page flip occurs. The vblank interval will be
* directly aligned to the page flip rate.
*
* Not all userspace content is suitable for use with variable refresh rate.
* Large and frequent changes in vertical front porch duration may worsen
* perceived stuttering for input sensitive applications.
*
* Panel brightness will also vary with vertical front porch duration. Some
* panels may have noticeable differences in brightness between the minimum
* vertical front porch duration and the maximum vertical front porch duration.
* Large and frequent changes in vertical front porch duration may produce
* observable flickering for such panels.
*
* Userspace control for variable refresh rate is supported via properties
* on the &drm_connector and &drm_crtc objects.
*
* "vrr_capable":
* Optional &drm_connector boolean property that drivers should attach
* with drm_connector_attach_vrr_capable_property() on connectors that
* could support variable refresh rates. Drivers should update the
* property value by calling drm_connector_set_vrr_capable_property().
*
* Absence of the property should indicate absence of support.
*
* "vrr_enabled":
* Default &drm_crtc boolean property that notifies the driver that the
* content on the CRTC is suitable for variable refresh rate presentation.
* The driver will take this property as a hint to enable variable
* refresh rate support if the receiver supports it, ie. if the
* "vrr_capable" property is true on the &drm_connector object. The
* vertical front porch duration will be extended until page-flip or
* timeout when enabled.
*
* The minimum vertical front porch duration is defined as the vertical
* front porch duration for the current mode.
*
* The maximum vertical front porch duration is greater than or equal to
* the minimum vertical front porch duration. The duration is derived
* from the minimum supported variable refresh rate for the connector.
*
* The driver may place further restrictions within these minimum
* and maximum bounds.
*
* The semantics for the vertical blank timestamp differ when
* variable refresh rate is active. The vertical blank timestamp
* is defined to be an estimate using the current mode's fixed
* refresh rate timings. The semantics for the page-flip event
* timestamp remain the same.
*/
/**
* drm_connector_attach_vrr_capable_property - creates the
* vrr_capable property